1. Field of Invention
The present invention relates to a device to securely fasten joints in pressure vessels, pipes, and other structures intended to isolate internal volumes from the external environment, or in structural joints. The present invention can join a blank cover to the end of a pressure vessel or it can join tubular members having internal passages. The present invention may be used in any application currently utilizing standard bolted flanges.
Specifically, the joint connecting mechanism is a clamp that fastens flange members together in an abutting engagement creating a pressure seal in order to isolate the joints' internal environment from its external environment. Some processes require frequent and rapid opening, closing and separation of flanged joints to allow access to internal volumes. The present invention relates to a automatic joint connecting means for quickly opening and closing joints by remote actuated means to allow separation of the flanges, in situations where work persons are put at risk performing the operation.
2. Description of Prior Art
In many cases, the prior art sacrifices safety to provide a quick acting joint connecting means. The prior art illustrates single point failure mechanisms where failure of only one member could cause the integrity of the joint to be catastrophically compromised. A higher standard of safety is dictated in today's world. The present invention provides multiple fasteners thus providing more safety. There is a need in industry to be able to automatically and remotely open and close a joint, and those with ordinary skill in the art can appreciate, providing redundancy in the fastening means adds difficulty. Many companies have developed quick acting connectors, but do not provide safety. Failure of these mechanisms prompted the American Society of Mechanical Engineers (ASME) to develop rules in their Boiler and Pressure Vessel Codes that give specific rules for adding safety to "Quick Acting" devices. In order to construct a quick acting connecting means in accordance with the Codes, these rules must be observed. Single acting fastening means and single point failure devices must have secondary back-up retaining elements that will assure joint integrity upon failure of the single acting fastening means or single point failure devices. Such retaining elements will complicate automated operation.
In some installations, pressure vessels, pipes, and structural joints are opened and closed manually under conditions hazardous to the work persons performing the operation. Most prior installations utilize joint connecting means consisting of bolted flanges that are very labor intensive. The basic closing nature of bolted flanges is illustrated in the American National Standards Institute (ANSI) Publication BB16.5. Other manually operated prior art for connecting joints consist of threaded, clamped, and breach-lock mechanisms. These labor intensive designs are not well suited in hazardous environments. After observing many "Quick Acting" joint connecting means, the present inventor realized that a safe, simple, and reliable, remotely operable, "Quick Acting" connecting means did not exist, and that a substantial need therefore went unmet in the industry. Although prior art provides simplicity, it does not provide sufficient safety. In analyzing paths of failure, the prior art contains unsafe single component failure paths that upon failure would catastrophically cause the opening of the connected joint. A logical method to create a safe connecting means is to incorporate redundancy in the fastening elements and to remove all single point failure devices from the connecting means.
Supplying redundancy in a automatic connecting means can be difficult and expensive. Those skilled in the art will appreciate the benefit of the simple automatic operation of the present invention which provides safe redundant fastening elements. Of course, the system should be operable manually as well, if necessary due to a power failure or other interruption. When compared to other automated joint connecting means, it can be noted that a significant economic benefit is realized with the present invention due to its simplicity. This simplicity directly relates to lower operating costs and shorter down time. In some processes, one day of down time can result in an economic loss far surpassing the initial cost of the automated connecting means. Therefore, simplicity in design is highly valued by end users of this technology. The prior art automated joint connecting device, providing redundancy in the fastening elements contain overly complex mechanisms compared to the present invention. In the process of providing redundancy, the prior art sacrifices simplicity, reliability, and economy.
U.S. Pat. Nos. 5,336,375; 4,820,384; 5,221,019; 5,294,157; 5,228,825; 5,048,876 and 4,726,109 are mechanisms designed to remotely assist or perform connecting and disconnecting of joints in pressure vessels. One can easily observe that these devices are overly complex and will inherently be unreliable, and will also be expensive to manufacture and maintain.
Pressure and temperature of the working fluid, mechanical loads, and mechanical properties of the sealing gaskets dictate the magnitude of the axial closing force. Gaskets that are suitable for moderate to high temperatures and pressures are not generally self-energized elastomers as required in U.S. Pat. No. 4,483,458 ("the '458 patent"). The mechanism disclosed in the '458 patent cannot supply axial joint closing force since it allows clamp halves and closing elements and the pressure vessel housing to move axially relative to each other. Another result stemming from this relative movement is fatigue damage. The '458 patent device will encounter unacceptable fatigue damage in cyclic operation, requiring frequent testing, repair, or replacement. The '458 mechanism also requires external guide frames and anchor locations for automatic actuators and supports, such as foundations, that are not practical or economical. It is much simpler and safer to connect a joint with a connecting means that closes onto itself independent of external devices. The '458 mechanism also lacks positive locking fastening elements that hold the clamp halves together, where, under pressure, predictable radial and tangential forces will force the clamp halves apart. Also, this device must take on different forms depending on its orientation with respect to gravity.
U.S. Pat. Nos. 3,310,329 and 4,347,944 disclose clamp connecting devices that consist of a unity clamp band automatically actuated to liberate and secure flange members. In both of these devices, unacceptably high stresses will be generated at the midpoint of the clamp band farthest away from the separation gap in the clamp band. The stresses will alternate between very high compression to very high tension as the clamp band is cycled from the open position to the closed position. All economical materials available for construction of the clamp band will undergo unacceptable fatigue damage, which will limit the useful life of these clamp connecting devices. The clamp band of these mechanisms can be compared to a single piece of wire which is bent back and forth until severe fatigue damage separates it into two pieces.
To avoid the problem of severe fatigue damage associated with aforementioned inventions, the prior art incorporated further degrees of freedom in the clamp band. High bending stresses are alleviated by hinges that interconnect segments of the clamp band. U.S. Pat. Nos. 2,982,437 and 5,455,739 illustrate such hinged clamp band connecting means. The hinge in these mechanisms is an unacceptable single point failure location. Further, the actuating means or drive that opens and closes the clamp band, is a single point failure location. U.S. Pat. No. 3,144,165 is another example of a single point failure mechanism. Such single point failure mechanisms are unsafe.
ASME Boiler and Pressure Vessel Codes give rules for the minimum acceptable safe construction of pressure retaining components. Prior automated clamp connecting means are unsafe and are not ASME Code compliant. Accordingly, there remains a need for an automated joint connecting means suitable for normal and extreme service that is simple, reliable, rugged, and above all, safe.